To enhance the thermal efficiency of building structure, Schöck developed an internal structural insulation system for floor slabs. In the present study, the internal insulation system is applied to slabs in the wall-slab structural system which is popular for high rise residential buildings in Korea. In order to verify the structural performance of the insulation system, structural testing is planned for slabs with the internal insulators under gravity loading condition and seismic in-plane loading condition. For the gravity loading test, twelve slab specimens are tested under monotonic vertical loading. Test parameters are type of internal insulator, slab thickness, and shear span. In the test, flexural moment capacity and shear capacity of the slabs are investigated. Crack pattern and deflection are also investigated. For the in-plane loading condition, cyclic in-plane shear loading is applied to three specimens. Test parameters are the number of insulator units. In this test, the in-plane shear capacity and load re-distribution capacity are investigated. Further, in-plane shear slip is investigated. The test results are used to prove the safety of the Schöck’s insulation system, providing experimental evidences. If any, design recommendations are provided based on current test results.